In recent years, following the growth of disks having an advantageous access speed as recording/reproducing mediums, it has been demanded to increase the winding speed of a tape and shorten fast forwarding/rewinding time to improve usability, by increasing the rotation speed of a motor of a magnetic recording tape which has a disadvantageous access speed.
As a tape medium running device, devices disclosed in Japanese Unexamined Patent Publication No. 2000-215559 and so on have been known. FIG. 10 shows a conventional tape medium running device.
Reference numeral 1 denotes a motor for driving a tape, reference numeral 2 denotes a take-up side reel where one end (beginning or end) of a magnetic recording tape is wound. The rotation of the motor 1 is conveyed to belts and gears and causes the magnetic recording tape to run. Reference numeral 3 denotes a supply side reel where the other end (beginning or end) of the magnetic recording tape is wound. The rotation of the take-up side reel 2 causes the magnetic recording tape to run and the magnetic recording tape is supplied to the take-up side reel 2.
Reference numeral 4 denotes a rotation detecting unit having an MR element (magnetic resistance element) which detects polarity (north pole and south pole) provided at predetermined intervals around the motor 1 and outputs a frequency signal, and the MR element outputs a signal of a frequency proportionate to the rotation speed of the motor 1. Reference numeral 5 denotes a winding diameter detecting unit which repeatedly calculates winding diameters based on the number of revolutions of the take-up side reel 2 and the supply side reel 3 and outputs a signal proportionate to a winding diameter.
Reference numeral 6 denotes a high reference speed calculating unit which outputs a high reference speed for setting the rotation speed of the motor 1 at a first speed for winding up the magnetic recording tape at high speed.
Reference numeral 7 denotes a low reference speed calculating unit which outputs a low reference speed for gradually reducing the rotation speed of the motor 1 from the first speed with passage of time and finally setting the rotation speed at a second speed for making stop at the end of the magnetic recording tape.
Reference numeral 8 denotes a winding diameter comparing unit which compares an output from the winding diameter detecting unit 5 and a winding diameter comparison reference value previously set in the unit, and outputs the results.
Reference numeral 101 denotes an abnormality detecting unit for detecting abnormality based on the output from the winding diameter detecting unit 5 and is constituted by a previous winding diameter detection output storage 35, an abnormal winding diameter judging unit 36, an abnormal winding diameter counter 37, and an abnormal winding diameter number comparing unit 38.
The previous winding diameter detection output storage 35 temporality stores a value just before the output from the winding diameter detecting unit 5 is updated, and outputs the value.
The abnormal winding diameter judging unit 36 compares the output from the winding diameter detecting unit 5 and the output from the previous winding diameter detection output storage 35. When the output from the winding diameter detecting unit 5 is larger than the output from the previous winding diameter detection output storage 35, abnormality is judged and a pulse is outputted.
The abnormal winding diameter counter 37 counts output pulses of the abnormal winding diameter judging unit 36 and outputs the results.
The abnormal winding diameter number comparing unit 38 compares the output from the abnormal winding diameter counter 37 and an upper limit of the number of abnormal winding diameter that is previously set in the unit, and the abnormal winding diameter number comparing unit 38 outputs the comparison results.
The output from the high reference speed calculating unit 6 and the output from the low reference speed calculating unit 7 are inputted to a reference speed setting unit 9 which outputs a signal selected based on the output from the winding diameter comparing unit 8 and an output signal of the abnormal winding diameter number comparing unit 38 that is an output signal of the abnormality detecting unit 101. One of the outputs is selected as a reference speed and is outputted.
The speed control unit 10 controls the speed of the motor 1 via the driving unit 11 and performs control so that the output from the rotation detecting unit 4 is close to a reference speed outputted from the reference speed setting unit 9.
First, when an instruction of winding up the magnetic recording tape from a take-up reel to a supply reel of a tape cassette is inputted to the tape medium running device, the reference speed setting unit 9 at the start of the fast forwarding and rewinding selects the output from the high reference speed calculating unit 6 and outputs the selected output to the speed control unit 10 as a reference speed, and the rotation speed of the motor 1 is controlled so as to wind up the magnetic recording tape at high speed (first speed).
In the case of rewinding, the supply reel of the tape cassette serves as the take-up side reel 2 and the take-up reel of the tape cassette serves as the supply side reel 3. Thus, the take-up side reel 2 winds up the magnetic recording tape from the supply side reel 3 in response to the rotation of the motor 1, and the take-up reel of the tape cassette that serves as the supply side reel 3 during winding decreases in winding diameter with passage of time.
As to the supply side reel 3 decreasing in winding diameter with passage of time, the winding diameter is detected by the winding diameter detecting unit 5 and is compared with the winding diameter comparison reference value in the winding diameter comparing unit 8.
The winding diameter comparison reference value inputted in the winding diameter comparing unit 8 is previously set so as to detect that the magnetic recording tape remaining on the supply side reel 3 comes close to the end. When the output from the winding diameter detecting unit 5 is smaller than the comparison reference value, the winding diameter comparing unit 8 judges that the magnetic recording tape comes close to the end.
During rewinding, at the timing when the winding diameter comparing unit 8 judges that the magnetic recording tape comes close to the end, the reference speed setting unit 9 which has recognized the judgment selects the output from the low reference speed calculating unit 7 so as to output a lower speed (second speed) than the first speed as the reference speed of the motor 1, and outputs the selected output to the speed control unit 10. The rotation speed of the motor 1 is automatically reduced to the lower speed (second speed) at a point before the end of the magnetic recording tape, and the tape is wound up.
The above operation is performed when a winding diameter is normally detected by the winding diameter detecting unit 5. When a winding diameter is erroneously detected by the winding diameter detecting unit 5, abnormality occurs so that an approach is made to the end of the magnetic recording tape without reducing the rotation speed of the motor 1 to the low speed (second speed) at a point before the tape end. In the event of such abnormality, the tape may be cut.
In the conventional art, the following operation is performed by the abnormality detecting unit 101 to avoid the above abnormality.
Namely, the abnormal winding diameter judging unit 36 repeatedly compares the latest winding diameter outputted from the winding diameter detecting unit 5 during rewinding and the previous winding diameter outputted from the winding diameter detection output storage 35. When the latest winding diameter is smaller than the previous winding diameter, it is judged that the winding diameter detecting unit 5 normally detects a winding diameter. Meanwhile, when the latest winding diameter is larger than the previous winding diameter, it is judged that the winding diameter detecting unit 5 detects a winding diameter in an abnormal manner.
Hence, when the winding diameter detecting unit 5 detects a winding diameter in an abnormal manner during rewinding, a pulse is outputted from the abnormal winding diameter judging unit 36 to the abnormal winding diameter counter 37.
In the abnormal winding diameter number comparing unit 38, the number of pulses, which are outputted from the abnormal winding diameter judging unit 36 and are counted by the abnormal winding diameter counter 37, is compared with an upper limit of the number of abnormal winding diameters that is previously set in the unit. When detection is made that the count of the abnormal winding diameter counter 37 is larger than the upper limit of the number of abnormal winding diameters, a signal indicating the malfunction of the winding diameter detecting unit 5 is outputted to the reference speed setting unit 9 by the abnormal winding diameter number comparing unit 38.
The reference speed setting unit 9, which recognizes that the abnormal winding diameter number comparing unit 38 detects the malfunction of the winding diameter detecting unit 5, forcibly reduces the rotation speed of the motor 1 to the lower speed (second speed) than the first speed regardless of an output signal of the winding diameter comparing unit 8, and the tape is wound up.
Although the above explanation discussed an example of rewinding, the similar operations are performed for fast forwarding as well.
The winding diameter comparison reference value, that is, a winding diameter position (hereinafter, referred to as a deceleration point) for starting reduction from the first speed to the second speed is set at a position having a smaller diameter on the supply side reel 3 to reduce a section for running at the second speed, so that time for fast forwarding or rewinding can be further shortened.
However, in the above conventional configuration, in the case where the latest winding diameter detected by the winding diameter detecting unit 5 is smaller than the previous winding diameter despite a fact that a winding diameter is erroneously detected by the winding diameter detecting unit 5, the deceleration point is not detected and the abnormality detecting unit 101 does not detect abnormality. Thus, reduction cannot be performed to the second speed and an approach is made to the end of the magnetic recording tape while the high speed (first speed) is maintained, resulting in a damage on the magnetic recording tape.
FIG. 11 shows a specific example.
As to a winding diameter of the supply side reel 3, FIG. 11 shows a graph of actual values and examples of values detected by the winding diameter detecting unit 5 with passage of time. The vertical axis indicates a winding diameter of the supply side reel 3 and the horizontal axis indicates elapsed time. An actual change in winding diameter is indicated by a broken line J, and winding diameters detected by the winding diameter detecting unit 5 are indicated by P1, P2, P3, P4, P5, P6, . . . . Points P5, P6, . . . , indicate points where winding diameters are erroneously detected due to fluctuations in load during running of the magnetic recording tape. The right side shows an enlarged view of a main part Q around the points.
When a winding diameter is erroneously detected due to fluctuations in load during running of the magnetic recording tape, in the conventional abnormality detecting unit 101, the detected winding diameter P5 is smaller than the previous winding diameter P4 stored in the previous winding diameter detection output storage 35 and is not detected as abnormal. At the winding diameters P5, P6, . . . , when such erroneous detections of winding diameters successively occur until the end of the magnetic recording tape, a deceleration point cannot be correctly detected. Although it is assumed that the high speed (first speed) is switched to the low speed (second speed) at a winding diameter Pn and an approach is made to the end of the magnetic recording tape, the approach is actually made to the end while the running speed of the magnetic record is kept at the high speed (first speed).
The present invention is devised to solve the conventional problem and has as its object the provision of a tape medium running device which can more correctly detect erroneous detection of a winding diameter in the winding diameter detecting unit 5, prevents an approach from being made to the end of the magnetic recording tape at high running speed and causing a damage on the tape, and can shorten fast forwarding/rewinding time.